The present disclosure relates generally to electronic circuits, and more particularly to a method and an apparatus for interfacing electronic devices having disparate operating voltages.
It is well known that electronic devices such as personal computers, televisions, digital cameras, personal entertainment devices, cellular phones, and similar others incorporate semiconductor integrated circuit (IC) chips, which are designed to operate at various voltage levels. Some IC chips such as processors may operate at lower voltages, e.g., approximately 1-2 volts, whereas some IC chips such as memory devices may operate at higher voltages, e.g., 3-5 volts. Presently, the operating voltage level for a selected IC chip may typically vary between approximately 0.8 volts to approximately 5.5 volts.
A voltage translator is an electronic circuit, which generates a voltage output signal having a desired voltage level in response to receiving a voltage input signal having a particular voltage level that is different than the desired voltage level. The voltage translator may also be referred to as a voltage converter, a voltage interface, a level shifter, and a voltage shifter. An automatic direction-sensing voltage translator enables a bi-directional exchange of digital logic signals between IC chips, circuits, or devices having disparate operating voltages.
FIG. 1A illustrates a circuit diagram of a pass-gate type voltage translator 100, according to prior art. The pass-gate type voltage translator 100 includes a port A 110 and a port B 120, each of which may be operable as an input or an output to support bi-directional signal transfer. An n-channel pass gate 130 drives high to low transition on the ports A 110 and B 120. A one-shot edge-rate accelerator 140 is operable to drive low to high transition on the ports A 110 and B 120. Pull up resistors Ra 150 and Rb 160 maintain the ports at a high level following a low to high transition. The pass-gate type voltage translator 100 provides a direct current (DC) drive to ground and therefore it is capable of supporting low-valued pull-up resistors Ra 150 and Rb 160 on the signal lines. Pass-gate type voltage translator 100 is typically used in open-drain applications at lower switching speeds on the order of 250 kHz or in push-pull applications at speeds on the order of 1 megahertz (MHz) to 10 Mhz. An open-drain application may include a wired-OR connection for a bus having multiple masters, e.g., the I2C bus. A push-pull application may include a bus having a single master at a particular instant in time.
FIG. 1B illustrates a circuit diagram of a fully-buffered type voltage translator 102, according to prior art. Transition circuits 170 and 180 are used to drive high-to-low or low-to-high transitions on the A 110 or B 120 ports when a corresponding transition is detected at either port. After the transition, buffered DC drive is applied to each port through a series resistor (Rsa 152 and Rsb 162) to hold the ports A 110 and B 120 at the current logic state until the next transition is detected. Fully-buffered type voltage translator 102 is typically used in applications requiring higher switching speeds on the order of 50 MHz to about 100 Mhz. However, the fully-buffered type voltage translator 102 is unable to operate in open-drain applications since it is unable to provide sufficient DC drive current compared to the voltage translator 100. Therefore, a need exists to provide a method and apparatus for providing voltage translation that is operable in both open-drain applications that are capable of operating at a lower switching speed and in push-pull applications that are capable of supporting higher switching speeds.